LPC47M172_07 SMSC [SMSC Corporation], LPC47M172_07 Datasheet - Page 225

• Manufacturer Part Number: LPC47M172_07
• Description: Advanced I/O Controller with Motherboard GLUE Logic
• Manufacturer: SMSC [SMSC Corporation]

SMSC LPC47M172
VECTOR
XOR Chain Testability Algorithm Example
An example algorithm for using the XOR chain for board test is shown below.
In this example, Vector 1 applies all "0s" to the chain inputs. The outputs being non-inverting, will
consistently produce a "1" at the XOR output on a good board. One short to VCC (or open floating to VCC)
will result in a "0" at the chain output, signaling a defect.
Likewise, applying Vector 6 (all "1s") to the chain inputs (given that there is an odd number of input signals
in the chain) will consistently produce a "0" at the XOR chain output on a good board. One short to VSS
(or open floating to VSS) will result in a "1" at the chain output, signaling a defect. It is important to note
that the number of inputs pulled to "1" will affect the chain output value. If the number of chain inputs
pulled to "1" is even, then a "1" will be seen at the output. If the number of chain inputs pulled to "1" is odd,
a "0" will be seen at the output.
Continuing with the example in Table 15.1, as the input pins are driven to "1" across the chain in
sequence, the XOR Output will toggle between "0" and "1." Any break in the toggling sequence (e.g.,
"1011") will identify the location of the short or open.
TEST
1
2
3
4
5
6
INPUT
PIN 1
0
1
1
1
1
1
Table 15.1 - XOR Test Pattern Example
INPUT
PIN 2
0
0
1
1
1
1
DATASHEET
Page 225
INPUT
PIN 3
0
0
0
1
1
1
INPUT
PIN 4
0
0
0
0
1
1
Advanced I/O Controller with Motherboard GLUE Logic
SMSC/Non-SMSC Register Sets (Rev. 01-11-07)
INPUT
PIN 5
0
0
0
0
0
1
OUTPUT
XOR
1
0
1
0
1
0
Datasheet